1. Field of the Invention:
The present invention concerns a vaulted cover equipped with a flange for the closing of an opening in a pressure vessel. More particularly, a cover for a pressure vessel that is held on by means of fastening elements leading through the flange. The cover is also equipped with a plurality of fittings welded thereon for the passage of steam pipes and with thermal insulation on the outside of the vaulted part of the cover and the cover flange. The thermal insulation consists of a thermal insulating material and a metallic covering applied to the thermal insulating material.
2. Background of the Prior Art:
Covers of the above-described type are used, for example, as closures for nuclear power station components, such as steam generators or coolers wherein high operating temperatures are prevalent. The covers must, therefore, be provided with thermal insulation. The design of such insulations present a difficult technical problem in itself, because the covers have numerous passages for steam pipes. Thus, the thermal insulation must be interrupted at these locations. Furthermore, the large differential thermal expansion of a vaulted cover of this type and of the metallic covering of its thermal insulation must be taken into consideration.
The state-of-the-art is represented by thermally insulating installations of walls exposed to a gaseous heat carrier. Thus, West German Offenlegungsschrift No. 21 59 781 discloses a type of thermal insulation for a reactor pressure vessel comprising several layers of highly porous metallic mesh and a number of thin metal sheets between the layers. The insulation is covered with retaining metal sheets fastened with bolts to the liner of the pressure vessel. A number of gaps due to manufacturing tolerances between the individual plates of the insulating material and the retaining sheets serve to connect the layers of mesh under pressure with the heat barrier.
In West German Offenlegungsschrift No. 29 14 040 another thermally insulating installation for surfaces of a nuclear reactor is described. It consists of several layers of a metal fabric or metal mesh separated by intermediate metal sheets which are combined into panels. The panels, covered at their circumference with a wrapper, are applied on one side against the surface to be protected and are covered on the other side with a supporting sheet. The panels are secured to the surface to be protected and to the supporting sheets by means of hollow bolts with nuts screwed onto their "hot" ends.
It has also been proposed to provide the fastening bolts of thermal insulations of this type with a spacer sleeve supported on one end by the surface to be protected and on the other end connecting with the stationarily supported retaining sheets of cover plates. The method of fastening them is such that the thermal expansion of the cover plates is not hindered.